After hearing the news, an emotional Oswalt, 49, spent much of Wednesday on social media celebrating that McNamara's years of hard work may have paid off. "I hope you got him, Michelle," he tweeted. "I hope THEY got him."

Gregg DeGuire / FilmMagic

Patton Oswalt poses with his late wife, true-crime author Michelle McNamara, in 2011

After McNamara died unexpectedly in her sleep in April 2016, Oswalt collaborated with a researcher and journalist to finish her book about the serial rapist and murderer believed to have killed at least 12 people and raped at least 45 people throughout California in the 1970s and 1980s.

The "A.P. Bio" star also told fans what made Wednesday's arrest all the more exciting is that it came just as filming begins on a new documentary based on his late wife's book.

"First day of filming on the documentary was yesterday’s book event in Naperville," he tweeted. "All of (McNamara's) family was there. Ended with me saying, 'He’s running out of time.' And now all of this. Surreal."